The invention relates to an optoelectronic distance sensor, particularly for projectile detonators, which emits directed optical pulses in the beat of a pulse generator and receives portions of these optical pulses which are scattered back from a surface in a receiving member which is oriented toward the point of impingement of the pulses on the surface and evaluates these pulses for putting out an actuation signal.
U.S. Pat. No. 3,013,855 describes a cloud recording device which emits a modulated light beam and processes its reflections in a tuned amplifier and a rectifier. The level of the resulting direct voltage is a measure for the light intensity appearing at the receiver. In order to assure that the device responds only to reflected light emitted by the transmitter, transmitter and receiver operate at a frequency of 120 Hz. No measures for noise suppression are provided.
U.S. Pat. No. 3,613,590 discloses a proximity fuse which emits a transmitting frequency in the direction toward a moving target. The received frequency is then a combination of the transmitted frequency and the Doppler frequencies. After mixing the transmitted frequency and the received frequency and filtering them through a lowpass filter, the resulting signal is utilized for the detonation. In this circuit, there are no noise problems which could not be solved with conventional means.
With an optoelectronic proximity sensor of the abovementioned type, the processing of the noise which is unavoidable due to the optical transmission is of particular significance in order to avoid error signals. An added complicating factor is that in many applications only a very small useful receiving energy can be expected since, on the one hand, the transmitting energy is already being kept as low as possible and, on the other hand, even poorly scattering surfaces must be detected, and that due consideration must be given to the fact that the noise resulting from foreign light sources may often be very strong.
It is the object of the invention to propose an optoelectronic proximity sensor in which the noise portions reaching the receiver are processed in such a manner that they will not lead to error signals, even if there is a low signal-to-noise ratio.